1. Field of the Invention
The invention relates to a magnetoresistive sensor, typically used in a magnetic disk drive; and, more specifically, the invention relates to a lead overlay magnetoresistive sensor having high sensitivity and high spatial resolution.
2. Description of the Background Art
Disk drives using magnetic recording of digital information store most of the data in contemporary computer systems. A disk drive has at least one rotating disk with discrete concentric tracks of data. Each disk drive also has at least one recording head typically having a separate write element and read element for writing and reading the data on the tracks. The read element in most contemporary disk drives includes a magnetic spin valve sensor. A magnetic spin valve sensor includes a sandwich of layers, also known as a sensor stack, including a ferromagnetic pinned layer, a nonmagnetic electrically conducting layer, and a ferromagnetic free layer. The resistance of the spin valve sensor changes with respect to the direction and magnitude of an applied magnetic field such as the field from a written magnetic transition on a disk. To detect the change in resistance, sense current is passed through the sensor through electrical leads. The electrical leads are also known as lead layers, or more simply, leads. Typically, hard bias material is disposed in layers near the ends of a sensor stack forming permanent magnets which impose a weak magnetic biasing field on the sensor stack.
A lead overlay magnetoresistive sensor has lead layers which overlay portions of the sensor stack. This arrangement offers the advantage that the effective trackwidth of the sensor is determined primarily by the distance between the two leads and not by the width of the sensor stack. In other magnetoresistive sensors the trackwidth also depends on such factors as the lateral. dimension of the sensor stack and the extent of magnetic hardening from the bias layers. Thus the lead overlay sensor offers an advantage of determining the trackwidth with one simple geometric parameter.
However, in practice, lead overlay sensors are subject to effective trackwidth widening due to sense current leakage from the leads into the sensor stack and hard bias layers away from the immediate vicinity of the active portion of the sensor stack. This effective trackwidth widening tends to decouple the relationship between the distance between leads and the effective trackwidth thus degrading one of the important potential advantages of a lead overlay sensor. Sense current leakage also adds parasitic resistance unrelated to magnetic signal and thus effectively degrades sensitivity.
Accordingly, what is needed is a lead overlay magnetoresistive sensor which concentrates most of the sense current through the ends of the leads in the immediate vicinity of the active portion of the sensor stack.